In connection with the manufacturing of mechanical prototypes, and especially during the production design processes, recent years have introduced various types of rapid prototyping techniques (RP) where three dimensional objects are manufactured by sequential cross section layers generated by a given illumination, sintering, setting or placing of material etc. on each cross section. The individual cross sections are e.g. generated as computer-aided designs. The advantage of RP is that the manufacturing of expensive molding tools for the design of the apparatus becomes superfluous for its manufacturing, just as difficult and time-consuming modifications of a molding tool may almost be completely avoided.
Also, various techniques have been made available for the manufacturing of relatively inexpensive and fast prototype or 0 series molding tools based on a manufactured Rapid Prototype.
One type of RP technique is used in e.g. stereolithographic apparatuses also called SLAs. This technique is based on the individual layers or cross sections of a prototype being manufactured by a photo-sensitive medium and hardened into one monolithic prototype by means of computer-aided illumination.
Apparatuses and techniques of the above-mentioned type are described in e.g. U.S. Pat. No. 4,575,330 where the illumination determined by the cross section is described as a laser drawing of each cross section or a transilluminating mask exposing the desired cross section.
Meanwhile, one of the disadvantages of the above-mentioned system is that the distribution of light over the cross section limits the design flexibility of the system as adjustments of existing sources of illumination are limited to certain system dimensions.
Thus, when manufacturing large-scale models, it is necessary to divide a given desired prototype into several prototype parts, manufacture these parts individually by separate runs and then finally complete the prototype by joining the parts by e.g. pasting.
However, this process involves a significant risk of running into technical problems and complications. It is necessary to take into account e.g. marginal problems for each prototype part as the tolerance level between adjacent prototype parts differs from the tolerance levels existing between each of the manufactured layers comprising the individual prototype parts. Meanwhile, this may be prevented by taking the proper precautions in relation to the illumination algorithms or by an actual mechanical manufacturing of the individual prototype parts if necessary. This compensation strategy would be particularly difficult on the “vertical level” and may e.g. lead to both under- and overillumination and consequently to tolerance or joining errors between the individual layers.
Problems could also arise in connection with the pasting of the prototype parts as the hardening of the paste may cause contractions or expansions in places where the paste is used. These changes in the hardening would often be of a non-linear character and thereby difficult to estimate or predict beforehand.
Another problem is that these joinings generally cause problems of strength when used on large-scale models.
An additional and significant problem is that common RPA materials (materials for Rapid Prototyping Apparatuses) such as acrylates and epoxy are quite hazardous making manual runs undesirable. In this connection, it should be mentioned that the joining of the individual prototypes must be carried out manually which adds to the costs and makes working conditions difficult. Also, due to the manual work to be carried out as described in accordance with the method above, the encapsulation of the apparatus makes it more difficult for the creators to carry out their work. This problem is even more outspoken in relation to the use of e.g. hazardous or directly toxic materials.
Finally, it should also be mentioned that the known method is quite time-consuming involving many hours and sometimes several days, depending on the size of the prototype.
EP 0 676 275 discloses a DMD-based stereolithographic device comprising a plurality of illumination modules, each module comprising a dedicated light source. By varying the number of the utilized modules, an arbitrary size and form of the illumination head may be obtained. However, the device has the disadvantage of being voluminous and quite expensive. Moreover, the mutual variation of the light sources results in a different degree of illumination of the various illuminated sub-areas, and consequently in both underexposure and overexposure of as well the vertical and horizontal plane of the illuminated surface.
The purpose of the invention is to create an RP technique and an RP apparatus that may be used for the manufacturing of e.g. large-scale prototypes while it is also the purpose of the invention to create a design system that may be applied in relation to the design of various types of RPA systems without requiring significant design modifications.